Improved Task Performance in Subjects with Retinal Prosthesis
Improved Task Performance in Subjects with Retinal Prosthesis
Background/aims To determine to what extent subjects implanted with the Argus II retinal prosthesis can improve performance compared with residual native vision in a spatial-motor task.
Methods High-contrast square stimuli (5.85 cm sides) were displayed in random locations on a 19″ (48.3 cm) touch screen monitor located 12″ (30.5 cm) in front of the subject. Subjects were instructed to locate and touch the square centre with the system on and then off (40 trials each). The coordinates of the square centre and location touched were recorded.
Results Ninety-six percent (26/27) of subjects showed a significant improvement in accuracy and 93% (25/27) show a significant improvement in repeatability with the system on compared with off (p<0.05, Student t test). A group of five subjects that had both accuracy and repeatability values <250 pixels (7.4 cm) with the system off (ie, using only their residual vision) was significantly more accurate and repeatable than the remainder of the cohort (p<0.01). Of this group, four subjects showed a significant improvement in both accuracy and repeatability with the system on.
Conclusion In a study on the largest cohort of visual prosthesis recipients to date, we found that artificial vision augments information from existing vision in a spatial-motor task.
Second Sight Medical Products (Sylmar, California, USA) has developed an epiretinal prosthesis aimed at partially restoring vision to people blinded by outer retinal degenerative diseases such as retinitis pigmentosa (RP). In these diseases, while the photoreceptors are compromised and there is anatomical remodelling of the remnant retina, post mortem anatomical studies have found that some bipolar and ganglion cells survive. Multiple acute and chronic studies in normal and degenerate animal models, and in human subjects, have shown that electrical stimulation of the retina can elicit percepts (phosphenes). More recently it has been demonstrated that stimulation with multiple electrodes can yield some level of spatial vision as measured by high-contrast square-wave grating tests.
The Argus II retinal prosthesis system (Second Sight Medical Products) consists of a surgically implanted 60-electrode stimulating microelectrode array consisting of 200 μm diameter disc electrodes, an inductive coil link used to transmit power and data to the internal portion of the implant, an external belt-worn video processing unit (VPU) and a miniature camera mounted on a pair of glasses (figure 1). The video camera captures a portion of the visual field and relays the information to the VPU. The VPU digitises the signal in real-time, applies a series of image processing filters, down-samples the image to a 6×10 pixelised grid, and creates a series of stimulus pulses based on pixel brightness values and look-up tables customised for each subject. The stimulus pulses are delivered to the microelectrode array via application-specific circuitry and a superior-temporally placed inductive radio frequency coil link allowing for wireless forward and reverse telemetry between intra and extra-ocular portions of the system.
(Enlarge Image)
Figure 1.
A schematic illustration showing the surgically implanted stimulating microelectrode array, and inductive coil telemetry link of the Argus II system (left). The external portions of the system consist of a video processing unit (VPU) (middle) and a miniature camera mounted on a pair of glasses (right).
Here we present results of a task requiring the integration of visual information afforded by the Argus II retinal prosthesis with motor movement—the localisation of a high contrast square target on a computer monitor.
Abstract and Introduction
Abstract
Background/aims To determine to what extent subjects implanted with the Argus II retinal prosthesis can improve performance compared with residual native vision in a spatial-motor task.
Methods High-contrast square stimuli (5.85 cm sides) were displayed in random locations on a 19″ (48.3 cm) touch screen monitor located 12″ (30.5 cm) in front of the subject. Subjects were instructed to locate and touch the square centre with the system on and then off (40 trials each). The coordinates of the square centre and location touched were recorded.
Results Ninety-six percent (26/27) of subjects showed a significant improvement in accuracy and 93% (25/27) show a significant improvement in repeatability with the system on compared with off (p<0.05, Student t test). A group of five subjects that had both accuracy and repeatability values <250 pixels (7.4 cm) with the system off (ie, using only their residual vision) was significantly more accurate and repeatable than the remainder of the cohort (p<0.01). Of this group, four subjects showed a significant improvement in both accuracy and repeatability with the system on.
Conclusion In a study on the largest cohort of visual prosthesis recipients to date, we found that artificial vision augments information from existing vision in a spatial-motor task.
Introduction
Second Sight Medical Products (Sylmar, California, USA) has developed an epiretinal prosthesis aimed at partially restoring vision to people blinded by outer retinal degenerative diseases such as retinitis pigmentosa (RP). In these diseases, while the photoreceptors are compromised and there is anatomical remodelling of the remnant retina, post mortem anatomical studies have found that some bipolar and ganglion cells survive. Multiple acute and chronic studies in normal and degenerate animal models, and in human subjects, have shown that electrical stimulation of the retina can elicit percepts (phosphenes). More recently it has been demonstrated that stimulation with multiple electrodes can yield some level of spatial vision as measured by high-contrast square-wave grating tests.
The Argus II retinal prosthesis system (Second Sight Medical Products) consists of a surgically implanted 60-electrode stimulating microelectrode array consisting of 200 μm diameter disc electrodes, an inductive coil link used to transmit power and data to the internal portion of the implant, an external belt-worn video processing unit (VPU) and a miniature camera mounted on a pair of glasses (figure 1). The video camera captures a portion of the visual field and relays the information to the VPU. The VPU digitises the signal in real-time, applies a series of image processing filters, down-samples the image to a 6×10 pixelised grid, and creates a series of stimulus pulses based on pixel brightness values and look-up tables customised for each subject. The stimulus pulses are delivered to the microelectrode array via application-specific circuitry and a superior-temporally placed inductive radio frequency coil link allowing for wireless forward and reverse telemetry between intra and extra-ocular portions of the system.
(Enlarge Image)
Figure 1.
A schematic illustration showing the surgically implanted stimulating microelectrode array, and inductive coil telemetry link of the Argus II system (left). The external portions of the system consist of a video processing unit (VPU) (middle) and a miniature camera mounted on a pair of glasses (right).
Here we present results of a task requiring the integration of visual information afforded by the Argus II retinal prosthesis with motor movement—the localisation of a high contrast square target on a computer monitor.
